Based on the provided SQL code, here’s a breakdown of what it does:

Problem Statement:

The user wants to retrieve data from a table (#B) that contains rows where RowNum is partitioned by SeqNo and DateOfBirth. The condition is that if Status='Completed' appears 2 times or more for a given RowNum, the corresponding row should be included in the output.

Solution:

The SQL code uses a Common Table Expression (CTE) to solve the problem. Here’s what it does:

1. It creates a temporary table (@Something) with columns matching those in the original data.
2. The data is inserted into this temporary table using insert ... values statements.
3. The main query selects all rows from the temporary table where there exists another row with the same SeqNo, has Status='Complete', and appears 2 times or more (using the having count(*) > 1 clause).

What’s happening in the query:

• The subquery inside the exists clause is used to check if a given row (s) has another row with the same SeqNo that also has Status='Complete'.
• The group by clause groups the rows by SeqNo, and the having count(*) > 1 clause checks if there are 2 or more such rows.

Why this query works:

The query works because it uses a self-join to compare each row with all other rows that have the same SeqNo. This allows it to detect when Status='Completed' appears 2 times or more for a given RowNum.

I hope this explanation helps! Let me know if you have any further questions.

Last modified on 2024-08-08